The present invention relates to the adhesive bonding of structural members and more specifically to a self-contained exothermic adhesive bonding system for applying thermoplastic or thermosetting resins.
Numerous existing bonding processes involve the application of either thermosetting or thermoplastic resins. Because such adhesive resins require heat energy to acquire their desired adhesive properties, it has heretofore been necessary to provide a separate external heating apparatus to melt a thermoplastic resin prior to application or to cure a thermosetting resin after application as a liquid. The need for a separate heating apparatus has reduced the convenience of such adhesives. In some cases it has even prevented their use in remote locations, such as under water or in a vacuum as exists in outer space.
To avoid this problem, U.S. Pat. No. 3,827,359 of Daughenbaugh, issued Aug. 6, 1974, proposes to provide a chemical substance which reacts with water to produce the heat energy needed to melt a thermoplastic resin. A mass of the resin is shaped to define a cavity which is partially filled with the reactive chemical substance. After the mass is placed against the hull of a ship, water is admitted into the cavity to react with the chemical substance, thereby producing heat to melt the mass. While this may be sufficient for attaching an explosive charge to a ship's hull, it would not provide a strong bond because the heat of the reaction could not be distributed evenly in such a system. Also, according to Daughenbaugh, a warmed resin is applied directly to a cold surface. Resin applied in this manner cools too rapidly to form an airtight bond. Daughenbaugh's system is further disadvantageous because it cannot be used in the absence of a water source.
H. H. Leonard, U.S. Pat. No. 4,001,152 discloses a mixture of a thermoplastic adhesive and a fuel in the form of a stick. The end is ignited, causing the adhesive to melt and drip onto a surface. The fuel is said to continue to burn, keeping the adhesive tacky for the application of an object to be joined to the surface. This can be used only in an atmosphere, such as air, which supports combustion.